The irregular association between crop production and soil bulk density (ρ) weakens the application of ρ for diagnosis and management of soil compaction. With the aim of evaluating this problem, this study introduce a mathematical procedure to simulate limits of ρ for water demand and soil penetration resistance (R) dynamic as a function of the time (t) of water extraction by crop evapotranspiration (E) of the soil layer explored by plant roots (L). Parameters of both penetration resistance and water retention curves of an Oxisol were used in the simulations of ρ and R for different conditions of E, t and L. The ρ varied inversely proportional to E and t and directly proportional to L. The equation of ρ also allows calculating the critical bulk density (ρc) calculated with the least limit water range (LLWR). Simulations done for up to six days of water extraction (t=6) in soil layers L with ρc from the LLWR for the Oxisol (1340kg m-3) indicate that the maximum R may increase from 2 to 8MPa, depending upon the E (0.002 to 0.006m d-1 ) and L (0.2 to 0.6m) conditions. Low values of R obtained when the E is small and L is large characterize conditions for normal crops production even the ρ is equal to the ρc.
soil compaction; evapotranspiration; modeling; soil management
